1. Field of the Invention
The present invention relates to a method of flattening a recess in a substrate, and more particularly to a method of flattening a recess on the sidewall of a trench in the substrate.
2. Description of the Prior Art
Capacitors are one type of component commonly used in the fabrication of integrated circuits, for example in DRAM circuitry. As integrated circuitry density has increased, there is a continuing challenge to maintain sufficiently high storage capacitance despite the decreasing capacitor area.
One technique used to improve the storage capacitance for the higher density DRAM cells is a stack capacitor. The capacitor structure of a stack capacitor is formed over the gate electrode of the transistor, rather than being in the same spatial plane as the gate electrode. To form the stack capacitor, a trench is formed in a sacrifice layer. The trench is then filled with a bottom electrode, a dielectric layer, and a top electrode. After that, the sacrifice layer is removed to form the stack capacitor.
Another technique proposed to improve the storage capacitance for higher density DRAM cells is a trench capacitor. The capacitor structure of a trench capacitor is formed within a trench.
For both the stack capacitor and the trench capacitor, greater capacitor surface area correlates to the trench design that is spatially deeper or wider. The trench width can not be enlarged due to the limited amount of substrate surface area for each memory cell. Thus, the depth of the trench must be increased by fabrication of the deeper trench. This deeper trench has high aspect ratio.
Moreover, besides the trenches in the capacitors, lots of elements also need trenches in their structures in integrated circuits. The trenches in those elements also have high aspect ratio in order to reach high density of the integrated circuits.
However, such high aspect ratio trenches usually have defects on their surfaces. For example, recesses on the sidewall of the trenches. Therefore, the performance of those elements may be deteriorated due to these defects.